In K. Billen, L. Federspiel, P. Schockmehl, B. Serban and W. Scherrel: Occupant Classification System for Smart Restrained Systems, SAE paper, 1999, page 33 through page 38, a seat mat having a sensor matrix is described, the sensor matrix being used for the continuous generation of a seat profile of different persons and objects. Features determined from the seat profile are used for occupant classification.
German Published Patent Application No.196 30 260 describes a system for detecting the presence of a live person, especially for detecting the occupation mode of a vehicle seat. In the process, an oscillation analysis is implemented, namely to determine in which frequency ranges an object or a person leads to signals.